METABOLISM OF MICROORGANISMS 



367 



tive of inositol, a vitamin which is found in many plant and animal 

 materials. 



Streptose is an unusual type of sugar. It has an aldehyde group 

 attached along the carbon chain to give a branching structure. The 

 aldehyde group can be reduced chemically to give the corresponding 

 alcohol. This derivative was thought for a time to be superior to strepto- 

 mycin clinically, but later work indicated that it had the same disad- 

 vantages as streptomycin. 



It has been suggested that streptomycin interferes with nucleic acid 

 metabolism. Since it is a basic substance, it may react with the acidic 

 groups of nucleic acid and form complexes that are not metabolized. 

 According to Umbreit, the mode of action of streptomycin is through 

 interference with pyruvic acid metabolism. This is a complex phenome- 

 non involving many enzymes, coenzymes, and chemical changes. If 

 streptomycin interferes with the pyruvate metabolism of microorganisms, 

 the question naturally arises as to why it does not affect the same metab- 

 olism in the animal? The explanation usually given is that streptomycin 

 does not penetrate the animal cell but remains in the extracellular fluid. 

 The bacteria infecting the animal cannot prevent the entrance of strepto- 

 mycin into their cells, hence their metabolism becomes deranged and 

 they die. 



Bacteria rapidly acquire resistance to streptomycin, and in such cells 

 Umbreit has found that the oxalacetate-pyruvate relation has disap- 

 peared. The bacteria have apparently been able to develop a new me- 

 tabolic pathway with which streptomycin does not interfere. A still more 

 puzzling phenomenon is the development of dependent bacteria, that is, 

 bacteria that will not grow unless streptomycin is added to the medium. 

 No satisfactory explanation has as yet been found for the development 

 of dependent strains. A possible explanation that has been advanced 

 is that the dependent strain produces so much of some metabolite that 

 it kills itself when no streptomycin is present to counteract the effect of 

 this metabolite. Some support for this theory is found in the increased 

 production of the metabolite para-aminobenzoic acid by certain bacteria 

 when sulfanilamide is added to the medium. 



Aureomycin and Terramycin. These two antibiotics are very similar 



CH3 



^H^ H C ?^ H V^ H N-CH3 



H. tlz"^ XT \ I TT \l 



ll-C^ ^C ^C^ ^C"^ X— OH 



H-C^ C C^ .ci*"^ .C-CONH 



(7)^ i^)\ (S)Y OH f') 



OH O OH 



Terramycin, C22H24N209 



2 



